Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method and an apparatus for transmitting a reference signal.
Related Art
Intensive researches are conducted in order to improve performance in terms of a capacity, transmission coverage, coordination between cells, and cost. Introduction of various technologies including small cell enhancement, macro cell enhancement, a new carrier type, machine type communication, and the like is discussed as a technological term in LTE release 12 for the performance improvement.
Enhancement of the capacity and the transmission coverage targeted by the LTE release 12 may be achieved by small cell enhancement based on inter-site carrier aggregation and inter-LTE-wireless local area network (WLAN) integration and the macro cell enhancement. As the size of the cell decreases, inter-cell movement of a UE frequently occurs, and as a result, the quantity of traffics signaled when the UE moves may increase. In order to solve the problem, signaling transmitted to a core network in a radio access network (RAN) is decreased by using the small cell enhancement to optimize a small cell.
The new carrier type (NCT) is a frame type which is newly defined differently from a legacy frame configuration. The NCT may be a carrier type optimized to the small cell, but may be applied to even the macro cell. The NCT may decrease overhead which occurs by transmitting a cell-specific reference signal (CRS) and demodulate a downlink control channel based on a demodulation reference signal (DM-RS). Energy of a base station may be saved and interference which occurs in a heterogeneous network (HetNet) by newly defining the NCT. Further, reference signal overhead which occurs at the time of transmitting data may be decreased by using the NCT. In more detail, the NCT maintains the existing frame structure (e.g., CP length, subframe structure, and duplex mode), but may be defined by a carrier which is different in a structure of an actually transmitted reference signal and is not backward compatible (to el-11 and below UEs).